In immunotherapy, immune cells such as NK cells, T cells and the like are taken out from plasma, expanded and/or activated ex vivo and administered to patients. At present, however, the effect varies even if the methodology is the same. The inconsistent effect may be attributable to the fact that immune cells insufficient in the expansion and/or activation are administered to patients, or the level of cytotoxicity of immune cells after expansion and/or activation is not measured in the process of the expansion and/or activation of immune cells. As a result, it is possible that the patients undergo a treatment, which may be ineffective, for a half year to one year or more.
As a method for measuring cell activity or viable cell number, a gamma ray measurement method using sodium chromate [51Cr] is known in the RI system, and release of lactic acid dehydrogenase and a time-resolved fluorometric method using terpyridine derivative chelate are known in the non-RI system (patent document 1, non-patent document 1). Since the gamma ray measurement method essentially requires use of RI facility capable of using gamma ray, it lacks broad utility and is difficult to adopt in the clinical site and the like. The lactic acid dehydrogenase-release assay has a problem of inaccurate measurement, since the background is too high due to a spontaneous release from effector cells in addition to the target cells. In addition, it is difficult to use the conventional Eu time-resolved fluorometric method using a terpyridine derivative chelate (e.g., bis(acetoxymethyl) 2,2′:6′,2″-terpyridine-6,6″-dicarboxylate: BATDA) as a standard measurement method, since release of chelate from the target cell is high and the results fluctuate widely depending on the cell condition.